ONE BIG EXPERIMENT

Much of the argument barely touches on the data - descending instead into personal attacks and accusations of conflicts of interest. Scientists on both sides talk of being taunted by their rivals. Both Cappuccio, who advocates less salt, and Staessen, the hypertension expert who has found risks in salt reduction, say they have been victimized or intimidated after publishing papers in scientific journals.

Salt-reduction advocate MacGregor points at one of his main opponents across the Atlantic, Morton Satin, director of science and research at the U.S.-based Salt Institute, who says reducing salt across whole populations may do more harm than good. “Imagine he’s wrong,” MacGregor said. “That would mean he’s responsible for millions of strokes worldwide. When he goes to sleep tonight, he might like to think about that.”

Satin hits back that the whole situation has left science behind. “Passions overtake an objective view of science… and we can have an entire society being led to believe something that doesn’t stack up.”

There is one thing the two sides appear to agree on: the matter could be settled by a large-scale - 20,000 to 30,000 people - randomized clinical trial with half allocated to a high and half to a low salt diet. To be done properly, the main protagonists agree, such a trial would need to run for several years. The huge numbers are needed so that all other possible factors - weight, age, fitness, quality of diet, and medical conditions - are roughly equal in both groups.

But salt-reduction advocates MacGregor and Cappuccio say such a trial would be prohibitively expensive, unnecessary, and may even be unethical. Again they draw comparisons with smoking. Since, in their view, the harms of salt are indisputable, asking people to be kept on a high salt diet for the purposes of a medical experiment would be equivalent to forcing people to smoke.

Alderman is enraged by such suggestions. “Any medical ethicist would say that before you impose changes you have to make sure they are safe and beneficial. If the science is uncertain, then how can it be unethical to do the right studies to answer the scientific questions? If you’re asking 300 million Americans and I don’t know how many millions of other people around the world to change their diet so dramatically, you ought to have overwhelming evidence that it’s a good idea and it’s safe.”

Until the row is settled, people’s salt intake will probably be guided by personal taste.

(Edited by Simon Robinson, Michael Williams and Sara Ledwith)

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By Kate Kelland, Health and Science Correspondent

LONDON